The purpose of this investigation is to identify, localize and precisely define the specificity of microbial lectins which may play a role in adherence/clearance mechanisms in the oral cavity. For our studies, we propose to synthesize photoactivatable glycopeptides bearing oligosaccharides of defined structure for use as lectin binding site-specific reagents. (125I-) photoactivatable glycopeptide reagents ((125I-) PAGP) will initially be employed in biding studies as probes to identify surface lectins in oral bacteria. Bacterial species examined will include freshly prepared clinical isolates as well as reference strains of Streptococcus mutans, Streptococcus sanguis, Streptococcus mitior, Actinomyces viscosus, Actinomyces naeslundii, Leptotrichia buccalis and Fusobacterium nucleatum. Previous studies have suggested that many of these strains appear to possess surface components which interact withgalactosides, yet they display very different adherent properties. Although these lectins may appear similar in terms of monosaccharide specificity, it is likely that these bacterial lectins possess the ability to recognize fine differences in more complex structure. We will use a direct binding assay employing (125I-) PAGP to investigate this possibility and to precisely define the specificities of the identified bacterial lectins. Quantitation of (125I) PAGP BINDING WILL BE BY DIRECT CELL COUNTING IN A GAMMA COUNTER, OR BY QUANTITATIVE DENSITOMETRY AFTER SDS-PAGE. In either case, specific binding will be confirmed by binding studies in the presence of 200-fold excess unlabeled PAGP. Kd and number of binding sites of each bacterial lectin will be calculated from Scatchard plot analysis of saturation curves. Additionally, we will characterize the affinity-labeled lectin-ligand complexes by SDS-PAGE and autofluorography, allowing us to compare the lectins on the basis of size. Regulation of lectin expression will next be evaluated using our prepared (125I-) PAGP reagents. We will examine the effects of phases of growth, and various cultural conditions on lectin expression by direct binding as above. Finally, we will use the PAGP reagents to define the surface location and distribution of the lectins by electron microscopy. For this purpose, the cytochemical marker horseradish peroxidase will be covalently-coupled to the PAPG.